Machine tool control



Dec 24, 1946- y F. A. BARNES 2,412,957

MACHINE TOOL'CONTROL Filed June 28', 1944 FREDERICK A. BARNES horneyPatented Dec. 2 4, 1946 MACHINE 'rooL coNTRoL Frederick A. Barnes,Cleveland Heights, Ohio, as-

signor to Bailey Meter Company, a corporation ot Delaware ApplicationJune 2s, 1944, sei-iai No. 542,541

(ci. sz-s) 3 Claims.

This invention relates to a control system for machine tools, and moreparticularly to a control system for governing` the relative rate ofmovement between the tool and the work piece of a machine tool.

One object of my invention is to provide a control system for a machinetool or the like whereby the tool may be advanced relative to the workpiece at a predetermined rate of speed.

A further object of my 'invention is to provide a control system for amachine tool whereby the tool may be advanced relative to the work pieceat a rate directly proportional to the speed of rotation c! the workpiece.

Still another object ofmy invention is to provide a control system for alathe whereby the tool will be moved longitudinally along the lathe at arate of speed directly proportional to the rate of l rotation of theWork piece.

A still further object of rmy invention is to provide a control systemfor a lathe whereby a thread of accurate pitch may be cut on a workpiece.

Another object of my invention is to provide a control system for alathe for advancing the tool along the workpiece at a rate of speeddirectly proportional to the rate of rotation of the work piece withoutemploying a lead screw or other mechanical means subject to wear.

A further object of my invention is to provide a control system for alathe whereby accurate screw cutting may be accomplished withoutdependence upon a. lead screw, the wear of ywhich affects the accuracyof the operation.

As a specific embodiment of my invention I preferably describe an enginelathe wherein the spindle is rotated at a preselected uniform speed byany means, either mechanical, electrical or hydraulic, and where thelongitudinal travel of the tool is accomplished by a hydraulicallyactuated servo-motor. The specic object of the invention being a controlof the two independent driving means to produce a preselected relationof speedtherebetween.

Further objects will be apparent from the description and drawing, inwhich:

Fig. 1 is a somewhat diagrammatic plan view of an engine latheillustrating the application of my invention thereto. y

Fig. 2 is a diagrammaticv representation 0f a pair of reversing valvesof Fig. 1 in an alternate position of operation.

Referring to Fig. l, I show therein my invention applied to an enginelathe l having a head stock or live center 2 adapted to be rotated atpreselected or desired speed by any suitable means, such as mechanicalmeans, an electric motor, a hydraulic motor, or the like. The lathe hasa tail stock or dead center 3 supported on a carriage 4 which ismanually adjustable along the bed of the lathe insuitable ways 5. As oneexample I show a motor 50 drivingthe head stock 2 through change gears5i. Also movable longitudinally along the bed of the lathe in suitableways 6 is a carriage 1. Mounted on the carriage 'l is a cross-slide 8movable on ways 9 transversely of the bed of the lathe.

The cross-slide 8 is provided with an adjustable tool support i0 inwhich is secured a tool ll. Transverse movements of the tool Il areproduced by manual adjustments. That i's, the tool is manually moved bymeans of the cross-slide 8 f on the ways 9 into engagement with the workpiece, the depth of cut is determinedv by the manual adjustment of thecross-slide transversely of the axis of the work piece and the shape ofthe cut is determined by the shape of the cutting tool. Longitudinalmovements of the tool il. that is movements of the tool parallel withthe axis of the work piece along the ways 6, are produced by means of a,hydraulic servo-motor generally indicated at I2 which is secured to thebed of the lathe and is connectedby means of a piston rod I3 to' thecarriage l.

Supported between the head stock 2 and the tail stock 3 is a work piecei4 on which, as illustrated, a machine thread is being cut. In orderthat the'thread will have a given pitch, as Well known to those familiarwith the art, it is necessary that the carriage 1, and accordingly thetool Ii..advance along the lathe a given amount per revolution of thework piece i4. In the ordinary lathe such advancement is obtained bygearing the carriage by means of a lead screw to the driving means ofthe head stock. Such an arrangement imposes a heavy load on the leadscrew however, which after a period of time wears so that the threads onthe work piece are not longer accurately formed. Furthermore,

. 3 In distinction to the ordinary means I employ a tracer mechanism,one form of which is generally indicated at I5 in Fig. 1 whereby Iestablish a pneumatic loading pressure for controlling the rate ofmovement of the carriage 1. The loading pressure so established variesfrom a predetermined value, which for convenience I call the normalvalue, in accordance with the departure of the rate of movement of thecarriage 1 from that desired, and such variations are effective torestore the rate of movement of the carriage 'l to that desired. Inother words, it may be said that so'long as the carriage 1 -moves at thedesired speed the loading pressure remains at the normal value, but uponthe slightest departure from the desired speed a corrsponding change inthe loading pressure occurs effective for restoring the speed of thecarriage 1 to that desired.

The tracer mechanism` I5 is preferably of the type described and claimedin my copending application Serial No. 542,920 to which reference may behad for full constructional and operational details. Suillce it to sayhere that the tracer mechanism comprises a body member I5 slideablymounted on ways I 6 transversely of the lathe. The body member I5 isadapted to be engaged by and positioned by a cam I1, which is adjustably(as at I8) mounted to the carriage 1 and positioned therewith throughthe agency of the piston rod I3. The cam I1 may be of relatively thinplate, massive enough for rigidity and to obviate distortion. Itscontact edge I9 is preferably a slow incline so that full longitudinaltravel of the carriage 1 results ina transverse movement of the tracerassembly a predetermined number of inches. The tracer body I5 is prefereably spring biased along the ways I5 toward the contact edge I9 so thatit is always in contact with the contact edge or proflle'of the cam I1.Extending from the tracer body I5 is a tracer arm or feeler 29 adaptedto engage the contact edge 2I of a template 22`.

The template 22 is positionable longitudinally of the lathe by the livecenter 2 through any convenient means such as a gear train 23. The gears23 may drive a worm 24 Journaled at one end in a fixed block 25 andtraveling a nut 26 to which the template 22v is fastened. The journalblock 25 is provided with rollers 21 guiding and supporting the template22 as it moves along. The template is adjustably fastened to its drivingnut 26 by means 28 so that the complete template may beremoved andreplaced with one having a different slope. The adjustment means 29 and30 allow slight adjustment of the position of any particular template 22relative to the driving nut 26 after the assembly has been fastenedtothe nut. 25 by means of thel screw 28. Inasmuch as the load on thescrew 24 is very light there is little tendency for wear, distortion ordeflection of the screw 24.

It isapparent that the requisite for cutting a uniform thread is theadvancement of the tool I I at a uniform speed while the work I4 isrotated at a uniform speed. Changes in the relative speeds determine thepitch of the thread. As the cams I9 and 2| are moved in oppositedirections past the tracer I5, 20 the relative position of the parts I5and 20 must remain constant if the thread is to be true. The deflectionof the tracer arm 29 relative the body I5 determines the bleed toatmosphere of air from the pipe 3I and consequently the speed of travelof the carriage and tool and therefore the pitch of the thread. Changeinthe relative speed of the work piece 4 and the tool, and consequentlychange in the pitch of the screw, is acomplished by adjusting the camsI9 and 2| relative to each other through the agency of the adjustingmeans I9, 29 and 30.

As previously mentioned, the tracer feeler 20 engages the contact edge2I of the template 22, while the tracer body I5 is engaged by thecontact edge I9 of the cam I1. Variation in distance between the contactsurfaces I9 and 2|, at the engagement line of the assembly I5, 20,results in more or less deflection of the feeler 20 relative to the bodyI5 from a predetermined or normal condition of deflection.

In general, the function of the tracer mechanisxn is to vary the rate ofdischarge to the atmosphere of a pressure fluid supplied to the assemblyI5 through the pipe 3| at the outlet side of a fixed orifice 32 to whichair under relatively higher' pressure is supplied from any convenientsource. Under normal conditions of deflection of the feeler 20 there isa constant small discharge of air to the atmosphere with a correspondingpredetermined pressure within the pipe 3I. As the deflection of thefeeler 20 relative to the body I5 increases or decreases the pressurewithin the pipe 3I is varied in predetermined degree. The object of thearrangement is for the tracer I5 to so control the servo-motorl2 as tomaintain constant the rate of discharge of fluid from the tracer I5 tothe atmosphere. The controlled air pressure representative of changes inthe deflection of the feeler 20 is effective upon a bellows 33 of afluid resistance assembly 34.

I show an o il pump 35 driven by a motor 36 and drawing its supply ofoil from a sump 31. Oil under pressure is supplied the servo-motor I2througha pipe 33. In connection with the hydraulic motor I2 and theadjustable fluid resistance assembly 34 I provide switching valves 39and 49 arranged to be moved together to either a normal" or a rapidtraverse" position of operation of the hydraulic motor I2. The valves 39and 40 are shown in Fig. 1 in the normal operating. position. Oil underpressure from a pump 35, driven by a motor 36, is forced through thepipe 38, the valve 49 and a pipe 4I to one end of the hydraulic motorI2. Oil from the other end of the motor I2 passes through a pipe 42, thevalve 40, the valve 39, the pipe 43, the adjustable fluid resistance 34and the pipe 44 tov a sump 31. The regulation of the variable resistance34 determines the rate of flow of oil through the pipe 42 andconsequently the rate of travel of the piston rod I3 toward the left ofthe drawing. Thus the rate of longitudinal travel of the tool I9 along fthe work piece I4 is controlled by the variable resistance 34 to passageof oil therethrough from the left-hand end of the motor I2.

In Fig. 2 I show the passage relation of the switching valves 39, 40 fora rapid return of the piston rod I 3 from left to right of Fig. l. Thatis for a'rapid return of the tool vIl to the beginning of its workingtravel. Oil from the pump 35 passes directly through the pipe 33, thevalve 40 and the pipe 42; while oil from the right-hand 1end of themotorA I2 passes directly through the parts of the assembly 34 that apredetermined resistance is offered by the assembly 34 to passage of oiltherethrough from the pipe 43.to the pipe 44. If the deflection ofthe.feeler 20 relative to the housing I increases or decreases therewill be a corresponding variation in the loading pressure eective withinthe bellows 33 and desirably a change in the rate of flow of oil fromthe pipe 43 to the pipe 44.

Three general conditions of operation may exist.

1. The speed of rotation of the work piece I4 is represented by the rateof longitudinal movement of the template 22. This is compared to therate of longitudinal movement of the cam II, which is representative ofthe travel `of the tool II along the work I4. If these two rates oftravel are in desired relation, then the distance between the surfacesI3 and 2| at the point of engagement of the feeler 20 remains constantand is such a distance asvto produce desired pressure within the pipe 3iand desired rate of travel of the tool II along the work piece.

2. If for some reason the rate of longitudinal travel of the tool II andcam I1 is faster than is desired. relative to the rate of longitudinaltravel of the template 22, then the contact surfaces I9, 2| will tend toapproach each other, producing a greater deflection of the feeler 20relative to the housing Il and resulting .in an increased pressurewithin the bellows 33. Such increase in pressure will tend to throttleoil the passage between the pipes 43 and 44 and to thereby decrease therate of travel of the piston rod I3 and cam I1 until duction may be usedas necessary to properly interrelate the various moving parts. Forinstance, the cam II might take a form other than that which I haveillustrated as being driven directly by the piston rod I3. In l'ikemanner the template 22 may take'a different form and be driven in adifferent manner Just so long as it is representative of the speed ofrotation of the spindle 2' and work piece I4. Declutching, high speedback travel and travel limits of common form may be incorporated inconnection with the movement of the template 22 to return it to aposition equivalent to the beginning of the cuting stroke of the tool IIfor a second or third passage of the tool along the work piece I4 ifsuch is required.

While I have illustrated and described certain preferred embodiments ofmy invention, it will be understood that they are by way of example onlyand that I am not to be limited thereto except as defined in thefollowing claims.

What I claim as newfand desire to secure b Letters Patent of the UnitedStates, is:

l. In combination with a lathe having a relatively movable tool and workpiece, means for rotating the work piece at substantially constantspeed, a carriage for the tool adapted to position the toollongitudinally along the work piece. a hydraulic'motor for moving thecarriage, a reciprocating cam, means for positioning the cam along arectilinear path by and with the carriage,

the rate of travel oi' the cam I1 and the template 22 are inpredetermined relation again.

3. It for some reason the rate of travel of the 4cam I1 is slower thanthe rate of travel of the and cam I1 relative to the template 22.

Thus upon any tendency of the rate of travel of the tool I I to departfrom predetermined relation to the rate of travel of the template 22(representative of the speed of rotation of the work Id) there will be acorrection through the agency of the servo-motor i2 to the rate oflongitudinal travel ofthe tool II and cam il. The tendency always beingto travel the tool along the work at as'peed in` predetermined relationto the rate of rotation of the work I8.

After a complete traverse of the work has been accomplished by the toolIl the operator moves the reversing valves 39, l0 to the position shownin Fig. 2, which removes the effect of the variable fluid resistance 34from the servo-motor I2, putting full oil pump pressure upon thelefthand end of the motor I2 and opening 4the a template disposed inopposing relation to and adjacent said cam,'means including a connectionwith the first named means to move the template along a path parallel tothat of said cam, and huid pressure means mounted between and underthevjoint control of said cam and template arranged to control thehydraulic motor.

2. The combination of claim 1 in which said fluid pressure meansincludes a two element valve normally discharging fluid to theatmosphere to establish a fluid pressure value representative ofrelatively movable tool and work piece, means for rotating the workpiece at substantially uniform speed, a carriage supporting the tool andmovable longitudinally of the work piece, motor means for moving thecarriage, f a relatively thin plate cam adapted to be positioned withthe carriage and thereby representative of speed of carriage movement, asecond relatively thin plate cam adapted to be positioned by the rstnamed means and thereby representative of the speed of rotation of thework piece,the two cams movable in substantial parallelism in a singleplane with their cam surfaces opposed, and means under the joint'control of the two cams controlling said motor means, `said motorcontrolling means comprising two interrelated members, one of saidmembers positioned by one of the cam surfaces and the other of saidmembers positioned by the other cam surface. the speed of travel of thecarriage being, responsive to variation in distance between said camsurfaces.

FREDERICK A. BARNES.

